Solvent-based ink composition for thermal inkjets comprising acetate solvent

ABSTRACT

A solvent-based ink composition for a thermal inkjet printhead. The ink composition comprises:
         (a) 20-80 wt. % of a compound of formula (C);       

     
       
         
         
             
             
         
       
         
         
           
             wherein:
           R 7  is a C 2-12  alkyl group interrupted with 0, 1, 2 or 3 oxygen atoms;   
         
             (b) 10-70 wt. % of a C 1-6  alcohol; and 
             (c) 0.01-25 wt. % of a colorant.

FIELD OF THE INVENTION

This invention relates to inkjet inks for thermal inkjet printers. Ithas been developed primarily to enable thermal inkjet printing onto awide range of substrates, including non-porous substrates.

CO-PENDING APPLICATIONS

The following applications have been filed by the Applicantsimultaneously with the present application Ser. Nos.:

-   12/557,517, 12/557,518, 12/557,520, 12/557,521, 12/557,525,    12/557,526, 12/557,527

The disclosures of these co-pending applications are incorporated hereinby reference.

CROSS REFERENCES

The following patents or patents applications filed by the applicant orassignee of the present invention are hereby incorporated bycross-reference.

6,755,509 7,222,943 7,188,419 7,168,166 7,086,719 7,669,980 7,832,8447,246,886 7,128,400 7,108,355 6,991,322 7,287,836 7,118,197 7,575,2987,364,269 7,077,493 6,962,402 7,686,429 7,147,308 7,524,034 7,118,1987,168,790 7,172,270 7,229,155 6,830,318 7,195,342 7,175,261 7,465,0357,108,356 7,118,202 7,510,269 7,134,744 7,134,743 7,182,439 7,210,7687,465,036 7,134,745 7,156,484 7,118,201 7,111,926 7,431,433 7,401,9017,468,139 7,581,822 7,328,978 7,328,978 7,334,876 7,147,306 7,448,7347,425,050 7,621,620 7,669,961 7,331,663 7,360,861 7,328,973 7,427,1217,407,262 7,303,252 7,249,822 7,537,309 7,311,382 7,360,860 7,364,2577,390,075 7,350,896 7,429,096 7,384,135 7,331,660 7,416,287 7,488,0527,322,684 7,322,685 7,311,381 7,270,405 7,303,268 7,470,007 7,399,0727,393,076 7,393,076 7,681,967 7,588,301 7,249,833 7,520,416 7,490,9277,331,661 7,524,043 7,300,140 7,357,492 7,357,493 7,566,106 7,380,9027,284,816 7,284,845 7,255,430 7,390,080 7,328,984 7,350,913 7,322,6717,380,910 7,431,424 7,470,006 7,585,054 7,347,534 7,441,865 7,469,9897,367,650 7,469,990 11/688,863 7,837,297 7,475,976 7,364,265 7,721,44112/014,767 12/014,768 12/014,769 7,832,838 7,862,162 7,758,14912/049,371 7,845,755 7,922,279 12/334,519 12/339,039

BACKGROUND OF THE INVENTION

Thermal bubble-forming inkjet printheads function by generating acertain amount of heat in the printing fluid contained in a nozzlechamber. This heat causes a bubble to form which eventually collapses asthe fluid is forced through a nozzle. The collapse of the bubble thencauses more fluid to enter the nozzle chamber for the same process tobegin again.

Due to the ability of water to form rapidly a bubble at elevatedtemperature, printers equipped with such thermal inkjet printheadstypically use water-based ink formulations.

However, although it is possible to print directly onto speciallytreated non-porous and semi-porous substrates, water-based inkjet inksare essentially limited to applications that use porous media, such asoffice papers and textiles. Accordingly, most printers that use thermalinkjet printheads are usually for the SOHO (small office home office)market.

In contrast, piezo printheads offer a wide degree of ink formulationflexibility, since droplet ejection occurs through a piezoelectric forcerather than a bubble forming mechanism. Because of this, many differentink chemistries can be used in piezo printheads, such as UV curable,solvent-based, hot-melt and oil-based, as well as water-based. Theoutput from the piezo printers is equally diverse, addressing a host ofgraphics market segments including packaging, wide-format displays, CDand glass decoration. Taking wide-format printing as an example, thereare a large number of solvent-based printers on the market all of whichuse piezo printheads. These print onto a range of media, including lowcost non-porous and semi-porous substrates such as uncoated vinyls andpolyesters.

The Applicant has developed a range of bend-actuated printheads, whichdo not rely on bubble formation for ink ejection and, like piezoprintheads, can be used with either aqueous or non-aqueous inks. Some ofthe Applicant's bend-actuated inkjet printheads are described in, forexample, U.S. Pat. Nos. 7,416,280; 6,902,255; US 2008/0129793; and US2008/0225082, the contents of which are herein incorporated byreference.

The present Applicant has also developed a range of thermalbubble-forming printheads, as described in, for example, U.S. Pat. Nos.6,755,509; 7,246,886; and 7,401,910, the contents of which areincorporated herein by reference.

The Applicant's thermal bubble-forming inkjet printers currently offerhigh-resolution and high-speed printing (e.g. 60 pages per minute at1600 dpi) of aqueous-based inks for SOHO markets. These aqueous-basedinks are suitable for printing onto porous and semi-porous media.However, it would be desirable to provide thermal bubble-forming inkjetprintheads, which can print ink onto a wider range of substrates,including non-porous media. This would allow thermal inkjet printheadsto compete fully with piezo printers, offering high-resolution andhigh-speed inkjet printing for a wide range of print media.

SUMMARY OF THE INVENTION

In a first aspect, there is provided a solvent-based ink composition fora thermal inkjet printhead, the ink composition comprising:

-   -   (a) 20-80 wt. % of a compound of formula (A);

wherein:

R¹ is C₁₋₆ alkyl; and

each of R², R³ and R⁴ is independently selected from H, C₁₋₆ alkyl,halogen, OH, and C₁₋₆ alkoxy;

-   -   (b) 10-70 wt. % of a C₁₋₆ alcohol;    -   (c) 0.01-25 wt. % of a colorant.

Optionally, R¹ is C₁₋₆ alkyl; and each of R², R³ and R⁴ is H.

Optionally, the compound of formula (A) is N-methyl-2-pyrrolidinone orN-ethyl-2-pyrollidinone.

Optionally, in all relevant aspects of the present invention, the C₁₋₆alcohol is ethanol.

Optionally, in all relevant aspects of the present invention, thecolorant is a dye or a pigment.

Optionally, in all relevant aspects of the present invention, the inkcomposition comprises 0.001-10 wt. % of a surfactant.

Optionally, in all relevant aspects of the present invention, thesurfactant is a nonionic surfactant.

Optionally, in all relevant aspects of the present invention, thesurfactant is non-polymeric.

Optionally, in all relevant aspects of the present invention, thecomposition does not comprise an acrylate polymer or copolymer.

Optionally, in all relevant aspects of the present invention, thecomposition does not comprise any polymers.

Optionally, the ink composition consists essentially of or consists onlyof the compound of formula (A), the C₁₋₆ alcohol and the colorant.

Optionally, the ink composition consists only of the compound of formula(A), the C₁₋₆ alcohol, the colorant and 0.01-10 wt. % of a surfactant.

In a second aspect, there is provided a method of ejecting ink from athermal inkjet printhead, the method comprising the steps of:

(i) supplying an ink to at least one nozzle chamber of the printhead;and

(ii) actuating a heater element in the nozzle chamber and heating theink to a temperature sufficient to form a bubble therein, therebycausing the ink to be ejected from a nozzle opening associated with thenozzle chamber,

wherein the ink is a solvent-based ink composition comprising:

-   -   (a) 20-80 wt. % of a compound of formula (A);

wherein:

R¹ is C₁₋₆ alkyl; and

each of R², R³ and R⁴ is independently selected from H, C₁₋₆ alkyl,halogen, OH, and C₁₋₆ alkoxy;

-   -   (b) 10-70 wt. % of a C₁₋₆ alcohol;    -   (c) 0.01-25 wt. % of a colorant.

Optionally, in all relevant aspects of the present invention, the ink isejected onto a non-porous or a semi-porous substrate.

Optionally, in all relevant aspects of the present invention, the inkadheres to the substrate.

Optionally, in all relevant aspects of the present invention, thesubstrate is a plastics substrate.

Optionally, in all relevant aspects of the present invention, thesubstrate is comprised of untreated vinyl or polyester.

Optionally, in all relevant aspects of the present invention, the heaterelement has a mass of less than 1 nanogram.

Optionally, in all relevant aspects of the present invention, the heaterelement is suspended in the ink chamber, such that the ink compositionenvelops the heater element.

Optionally, in all relevant aspects of the present invention, anactuation energy for the heater element is less than 500 nJ.

Optionally, in all relevant aspects of the present invention, theprinthead is a stationary pagewidth printhead.

Optionally, in all relevant aspects of the present invention, theprinthead comprises at least 50,000 nozzles.

In a third aspect, there is provided a solvent-based ink composition fora thermal inkjet printhead, the ink composition comprising:

-   -   (a) 20-80 wt. % of a compound of formula (B);

wherein:

-   -   R⁵ is a C₁₋₆ alkyl group and R⁶ is a C₁₋₆ alkyl group; or    -   R⁵ and R⁶ are together joined to form a C₃₋₁₂ cycloalkylene        group;    -   (b) 10-70 wt. % of a C₁₋₆ alcohol;    -   (c) 0.01-25 wt. % of a colorant.

Optionally, the compound of formula (B) is methylethylketone.

Optionally, the compound of formula (B) is cyclohexanone.

In a fourth aspect, there is provided a method of ejecting ink from athermal inkjet printhead, the method comprising the steps of:

(i) supplying an ink to at least one nozzle chamber of the printhead;and

(ii) actuating a heater element in the nozzle chamber and heating theink to a temperature sufficient to form a bubble therein, therebycausing the ink to be ejected from a nozzle opening associated with thenozzle chamber,

wherein the ink is a solvent-based ink composition comprising:

-   -   (a) 20-80 wt. % of a compound of formula (B);

wherein:

-   -   R⁵ is a C₁₋₆ alkyl group and R⁶ is a C₁₋₆ alkyl group; or    -   R⁵ and R⁶ are together joined to form a C₃₋₁₂ cycloalkylene        group;    -   (b) 10-70 wt. % of a C₁₋₆ alcohol;    -   (c) 0.01-25 wt. % of a colorant.

In a fifth aspect, there is provided a solvent-based ink composition fora thermal inkjet printhead, the ink composition comprising:

-   -   (a) 20-80 wt. % of a compound of formula (C);

wherein:

-   -   R⁷ is a C₂₋₁₂ alkyl group interrupted with 0, 1, 2 or 3 oxygen        atoms;    -   (b) 10-70 wt. % of a C₁₋₆ alcohol;    -   (c) 0.01-25 wt. % of a colorant.

Optionally, R⁷ is a C₄₋₈ alkyl group interrupted with 0, 1 or 2 oxygenatoms.

Optionally, the compound of formula (C) is selected from the groupconsisting of: hexyl acetate; carbitol acetate; butyldiglycol acetate;and methoxypropyl acetate.

In a sixth aspect, there is provided a method of ejecting ink from athermal inkjet printhead, the method comprising the steps of:

(i) supplying an ink to at least one nozzle chamber of the printhead;and

(ii) actuating a heater element in the nozzle chamber and heating theink to a temperature sufficient to form a bubble therein, therebycausing the ink to be ejected from a nozzle opening associated with thenozzle chamber,

wherein the ink is a solvent-based ink composition comprising:

-   -   (a) 20-80 wt. % of a compound of formula (C);

wherein:

-   -   R⁷ is a C₂₋₁₂ alkyl group interrupted with 0, 1, 2 or 3 oxygen        atoms;    -   (b) 10-70 wt. % of a C₁₋₆ alcohol;    -   (c) 0.01-25 wt. % of a colorant.

In a seventh aspect, there is provided a solvent-based ink compositionfor a thermal inkjet printhead, the ink composition comprising:

-   -   (a) 20-80 wt. % of a compound of formula (D);

wherein:

-   -   each of R⁸ and R⁹ is independently selected from a C₁₋₁₂ alkyl        group interrupted with 0, 1, 2 or 3 oxygen atoms; or    -   R⁸ and R⁹ are together joined to form a C₃₋₁₂ cycloalkylene        group;    -   (b) 10-70 wt. % of a C₁₋₆ alcohol;    -   (c) 0.01-25 wt. % of a colorant.

Optionally, at least one of R⁸ and R⁹ includes one or more oxygen atominterruptions.

Optionally, the compound of formula (D) is selected from the groupconsisting of: dipropylene glycol monomethyl ether, dipropylene glycoldimethyl ether, diethylene glycol diethyl ether, propylene glycol butylether, dipropylene glycol dimethyl ether, dipropylene glycol butylether, diethylene glycol monopropyl ether, propylene glycol propylether, tetraethylene glycol dimethyl ether, methyl butyl ether,tripropylene glycol methyl ether, tetrahydrofuran, and tetrahydropyran.

In an eighth aspect, there is provided a method of ejecting ink from athermal inkjet printhead, the method comprising the steps of:

(i) supplying an ink to at least one nozzle chamber of the printhead;and

(ii) actuating a heater element in the nozzle chamber and heating theink to a temperature sufficient to form a bubble therein, therebycausing the ink to be ejected from a nozzle opening associated with thenozzle chamber,

wherein the ink is a solvent-based ink composition comprising:

-   -   (a) 20-80 wt. % of a compound of formula (D);

wherein:

-   -   each of R⁸ and R⁹ is independently selected from a C₁₋₁₂ alkyl        group interrupted with 0, 1, 2 or 3 oxygen atoms; or    -   R⁸ and R⁹ are together joined to form a C₃₋₁₂ cycloalkylene        group;    -   (b) 10-70 wt. % of a C₁₋₆ alcohol;    -   (c) 0.01-25 wt. % of a colorant.

In a further aspect, there is provided a printer comprising:

-   -   an ink reservoir containing a respective ink; and    -   a thermal inkjet printhead in fluid communication with the ink        reservoir,        wherein the ink is any one of the solvent-based ink compositions        described above.

Optionally, the thermal inkjet printhead comprises a plurality ofnozzles, each of the plurality of nozzles comprising:

a nozzle chamber containing the ink, the nozzle chamber having a nozzleopening for ejection of the ink; and

a heater element in contact with the ink, the heater element beingconfigured for heating the ink to a temperature sufficient to form abubble therein and thereby cause ejection of the ink from the nozzleopening.

In a further aspect, there is provided an ink cartridge for a thermalinkjet printhead, the ink cartridge containing any one of thesolvent-based ink compositions described above.

Optionally, the ink cartridge comprises a thermal inkjet printheadintegrated therewith.

In a further aspect, there is provided a substrate having any one of theink compositions described above disposed thereon.

Optionally, the substrate is a semi-porous or non-porous substrate.

Optionally, the substrate is a vinyl substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

Optional embodiments of the present invention will now be described byway of example only with reference to the accompanying drawings, inwhich:

FIG. 1 is a perspective view of part of a thermal inkjet printhead;

FIG. 2 is a side view of one of the nozzle assemblies shown in FIG. 1;and

FIG. 3 is a perspective of the nozzle assembly shown in FIG. 2.

FIG. 4 is perspective view of a thermal inkjet print engine.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides solvent-based ink compositions, which maybe jetted from a thermal inkjet printhead of the type that rapidlygenerates a bubble in each nozzle chamber in order to eject ink. Theoverwhelming preference of the prior art is to eject aqueous inkcompositions from thermal inkjet printheads. However, as foreshadowedabove, aqueous ink compositions limit the number of applications inwhich thermal inkjet printheads may be used. The present invention,which makes use of non-aqueous ink compositions, expands the number ofpossible applications for thermal inkjet printheads by enabling suchprintheads to print ink which adheres to non-porous and semi-porousprint media. Hence, the use of thermal inkjet printheads in wide-formatand other markets is a realistic possibility using the presentinvention.

The ink compositions according to the present invention arecharacterized by their relative simplicity, especially when compared totheir solvent-based counterparts typically used in piezo printheads. Atypical solvent-based ink composition used in piezo printheads has asolvent system comprised of about five or more different solvents.Moreover, these solvent-based ink compositions usually comprise one ormore polymers (e.g. acrylate polymers) to aid dispersion of colorant(s)in the ink. It is an advantage of the present invention that the solventsystem comprises only two solvents and does not normally comprise anypolymers.

The absence of polymers not only reduces cost, but also minimizes thepropensity for non-volatile residues to build up on the thermal heaterelements in the printheads (otherwise known as “kogation”). It issurprising that relatively simple solvent-based ink compositions can jeteffectively and adhere to non-porous substrates in the absence ofpolymers and, in particular, acrylate polymers.

The ink compositions of the present invention generally comprise threemain components, each of which will be discussed in more detail. Thefirst component is a solvent, which promotes adhesion of the ink tonon-porous surfaces (e.g. vinyl surfaces). The second component promotesbubble formation in the thermal printhead. The third component is acolorant, which may be either a dye or pigment.

Although inks may be formulated using only these three components, afourth component may additionally be present for improving the filmappearance of the ink on non-porous media.

The first and second components together typically make up at least 70%wt. %, at least 80 wt. % or at least 90 wt. % of the ink composition.

The amount of the first component (“adhesion-promoting solvent”) is inthe range of 20 to 80 wt. %, based on the total weight of the inkcomposition. Optionally, the amount of first component is in the rangeof 30 to 60 wt. %, or optionally 40 to 50 wt. %.

The amount of the second component (“bubble-promoting solvent”) is inthe range of 10 to 70 wt. %, based on the total weight of the inkcomposition. Optionally, the amount of second component is in the rangeof 30 to 60 wt. %, or optionally 40 to 50 wt. %.

The ratio of the first and second components may be in the range of 3:1to 1:3, optionally 2:1 to 1:2 or optionally 1.5:1 to 1:1.5. In apreferred ink composition, the first and second components are presentin approximately equal amounts i.e. about a 1:1 ratio.

The amount of the third component (“colorant”) is in the range of 0.01to 25 wt. %, based on the total weight of the ink composition. The exactamount of third component will usually depend on whether the colorant isa dye or pigment, as well as the characteristics of the dye or colorant(e.g. optical density) and other printing parameters (e.g. droplet size,dot density etc). Optionally, the amount of third component is in therange of 0.1 to 10 wt. %, or optionally 1 to 5 wt. %.

The amount of fourth component (“film appearance improver”), whenpresent in the ink composition, is in the range of 0.01 to 10 wt. %.Optionally, the amount of fourth component is in the range of 0.05 to 5wt. %, or optionally 0.1 to 1 wt. %.

The ink composition may consist essentially of the first, second andthird components. In other words, the first, second and third componentstogether may comprise at least 90 wt. %, at least 95 wt. %, or least 98wt. % of the ink composition.

In some embodiments, the ink composition may consist of only the first,second and third components. In other embodiments, the ink compositionmay consist of only the first, second, third and fourth components.

Typically, the ink composition does not contain any acrylate polymers,which are usually used in solvent-based ink compositions described inthe prior art. Alternatively, the ink composition may not contain anypolymers whatsoever.

Adhesion-Promoting Solvent

The Applicant has observed that certain types of solvent interactstrongly with non-porous substrates, whilst also being jettable from athermal inkjet printhead. In particular, some solvents adhere stronglywith a vinyl print media and leave a film impression, which cannot beeasily removed. By contrast, water and ethanol do not leave anyimpression on vinyl surfaces.

A first type of adhesion-promoting solvent is of formula (A):

-   wherein:-   R¹ is C₁₋₆ alkyl; and-   each of R², R³ and R⁴ is independently selected from H, C₁₋₆ alkyl,    halogen, OH, and C₁₋₆alkoxy.

Typical examples of a solvent of formula (A) areN-methyl-2-pyrrolidinone (NMP) and N-ethyl-2-pyrollidinone (NEP).

A second type of adhesion-promoting solvent is of formula (B):

wherein:

-   -   R⁵ is a C₁₋₆ alkyl group and R⁶ is a C₁₋₆ alkyl group; or    -   R⁵ and R⁶ are together joined to form a C₃₋₁₂ cycloalkylene        group;

Typical examples of a solvent of formula (B) are methyl ethyl ketone(MEK), methyl propyl ketone, methyl butyl ketone, cyclohexanone,cyclopentanone, cycloheptanone, cyclooctanone and isophorone.

A third type of adhesion-promoting solvent is of formula (C):

wherein:

-   -   R⁷ is a C₂₋₁₂ alkyl group interrupted with 0, 1, 2 or 3 oxygen        atoms.

Typical examples of a solvent of formula (C) are hexyl acetate, ethylacetate, butyl acetate, carbitol acetate[2-(2-ethoxyethoxy)ethylacetate], isooctyl acetate, butyl carbitol acetate[2-(2-butoxyethoxy)ethyl acetate], butyldiglycolacetate[2-(2-butoxyethoxy)ethyl acetate], and methoxypropyl acetate.

A fourth type of adhesion-promoting solvent is of formula (D):

wherein:

-   -   each of R⁸ and R⁹ is independently selected from a C₁₋₁₂ alkyl        group interrupted with 0, 1, 2 or 3 oxygen atoms; or    -   R⁸ and R⁹ are together joined to form a C₃₋₁₂ cycloalkylene        group.

Typical examples of a solvent of formula (D) are dipropylene glycolmonomethyl ether, dipropylene glycol dimethyl ether, diethylene glycoldiethyl ether, propylene glycol butyl ether, dipropylene glycol dimethylether, dipropylene glycol butyl ether, diethylene glycol monopropylether, propylene glycol propyl ether, tetraethylene glycol dimethylether, methyl butyl ether, tripropylene glycol methyl ether,tetrahydrofuran and tetrahydropyran.

The term “alkyl” is used herein to refer to alkyl groups in bothstraight and branched forms. Unless stated otherwise, the alkyl groupmay be interrupted with 1, 2 or 3 heteroatoms selected from O, NH or S.For example, an O atom interruption in a C-C bond provides an ether.Alternatively, an O atom interruption in a C—H bond provides an alcohol.Hence, ethers and alcohols are within the ambit of “alkyl” as definedherein.

Unless stated otherwise, the alkyl group may also be interrupted with 1,2 or 3 double and/or triple bonds. However, the term “alkyl” usuallyrefers to alkyl groups having no double or triple bond interruptions.Where alkenyl, ether, alkoxy etc. groups are specifically mentioned,this is not intended to be construed as a limitation on the definitionof “alkyl” above.

Where reference is made to, for example, C₁₋₆ alkyl, it is meant thealkyl group may contain any number of carbon atoms between 1 and 6. Byway of example, C₁₋₆ alkyl may encompass groups, such as methyl, ethyl,propyl (including n-propyl, isopropyl etc), butyl (including n-butyl,t-butyl etc), pentyl, hexyl, butenyl, pentenyl, hexenyl, iso-propenyl,methoxypropyl, ethoxyethyl, methoxymethyl, ethoxybutyl etc.

The term “alkyl” usually refers to acyclic alkyl groups, but it may alsoinclude cycloalkyl groups.

As used herein, the term “cycloalkyl” includes cycloalkyl,polycycloalkyl, and cycloalkenyl groups, as well as combinations ofthese with linear alkyl groups (e.g. a cycloalkyl group including alkylsubstituent(s) attached to the ring). The cycloalkyl group may beinterrupted with 1, 2 or 3 heteroatoms selected from O, N or S. Suchcylcoalkyl groups may be in the form of a cycloalkyl ring substitutedwith, for example, alkoxy group(s) or they may be in the form of aheterocylocalkyl group. Examples of heterocycloalkyl groups arepyrrolidino, morpholino, piperidino etc. However, the term “cycloalkyl”usually refers to cycloalkyl groups having no heteroatom interruptions.Examples of cycloalkyl groups include cyclopentyl, cyclohexyl,cyclohexenyl, cyclohexylmethyl and adamantyl groups.

The term “halogen” or “halo” is used herein to refer to any of fluorine,chlorine, bromine and iodine. Usually, however, halogen refers tochlorine or fluorine substituents.

Bubble-Forming Solvent

Although the adhesion-promoting solvents described above have aninherent bubble-forming characteristic (as well as good adhesion ofvinyl substrates), the ability of these solvents to form bubbles in athermal inkjet device is improved markedly by the addition of a C₁₋₆alcohol. For the avoidance of doubt, the term “C₁₋₆ alcohol” as usedherein refers to alcohol compounds having from 1 to 6 carbon atoms andonly one hydroxyl group.

Examples of suitable C₁₋₆ alcohols are methanol, ethanol, propanol (e.g.isopropanol), butanol, pentanol and hexanol. A preferred C₁₋₆ alcoholfor use as the bubble-forming solvent in the present invention isethanol.

Colorant

As mentioned herein, the colorant may be a dye or a pigment. It is anadvantage of the present invention that the ink composition maycomprises either a dye-based colorant or a pigment-based colorant.

Inkjet colorants will be well-known to the person skilled in the art andthe present invention is not limited to any particular type of dye orpigment.

Pigments suitable for use in the present invention may be inorganicpigments or organic pigments. Examples are carbon black, Cadmium Red,Molybdenum Red, Chrome Yellow, Cadmium Yellow, Titan Yellow, chromiumoxide, Viridian, Titan Cobalt Green, Ultramarine Blue, Prussian Blue,Cobalt Blue, diketopyrrolo-pyrrole, anthraquinone, benzimidazolone,anthrapyrimidine, azo pigments, phthalocyanine pigments (includingnaphthlocyanine pigments), uinacridone pigments, isoindolinone pigments,dioxazine pigments, indanthrene pigments, perylene pigments, perinonepigments, thioindigo pigments, quinophthalone pigments, and metalcomplex pigments. Some specific examples of suitable pigments, which maybe used in the present invention, are Pigment 15:3, Pigment V19, PigmentY151 and Pigment PK-7.

Dyes suitable for use in the present invention include azo dyes, metalcomplex dyes, naphthol dyes, anthraquinone dyes, indigo dyes, carboniumdyes, quinone-imine dyes, xanthene dyes, cyanine dyes, quinoline dyes,nitro dyes, nitroso dyes, benzoquinone dyes, naphthoquinone dyes,phthalocyanine dyes (including naphthalocyanine dyes), and metalphthalocyanine dyes (including metal naphthalocyanine dyes).

Some specific examples of suitable dyes, which may used in the presentinvention, are Solvent red 8, Solvent blue 70, Solvent yellow 82 andSolvent black 27.

The pigments and dyes can be used either individually or as acombination of two or more thereof.

The average particle size of pigment particles is optionally in therange of 50 to 500 nm.

Film Appearance Improver

A fourth component may be included in the ink compositions of thepresent invention in order to improve the film appearance of the inkwhen deposited on a non-porous substrate e.g. vinyl or polyestersubstrate.

Usually, the film appearance improver is a surfactant contained in theink composition in an amount of from 0.001 to 10 wt. %. Optionally, thesurfactant is contained in an amount of from 0.01 to 5 wt. %, or from0.05 to 2 wt. %, or from 0.1 to 1 wt. %.

The surfactant, when present, is typically a nonionic surfactant.Typically, the nonionic surfactant is non-polymeric.

Surfactants suitable for use in the present invention includefluorosurfactants (e.g. ethoxylated fluorosurfactants). Some specificexamples of fluorosurfactants suitable for improving the film appearanceof ink compositions according to the present invention are Zonyl®FSO andZonyl® FSO-100.

Other specific examples of surfactants suitable for improving the filmappearance of ink compositions according to the present inventioninclude Tego Wet® 450, Tegoglide® 410, Twin®400, Tego Wet® 270 andTegoglide® 482.

Although ink compositions according to the present inventionadvantageously provide excellent print quality and jettability in theabsence of polymer additives (especially acrylate polymers), certainpolymers may improve the film appearance of the ink when printed. Forexample, vinyl polymers may improve the film appearance of the ink whenprinted on vinyl substrates. An example of a vinyl polymer additive is ahigh molecular weight copolymer of vinyl chloride and vinyl acetate(e.g. UCAR™ VYHH). Such polymer additives may be included in an amountof from 0.01 to 5 wt. %, or from 0.05 to 2 wt. %, or from 0.1 to 1 wt.%. However, it is usually preferred to provide ink compositions, whichare completely free of any polymer additives.

Thermal Inkjet Printheads

The solvent-based ink compositions according to the present inventionare designed to be used with thermal inkjet printheads. There nowfollows a brief description of one of the Applicant's thermal inkjetprintheads, as described in U.S. Pat. No. 7,303,930, the contents ofwhich is herein incorporated by reference.

Referring to FIG. 1, there is shown part of printhead comprising aplurality of nozzle assemblies. FIGS. 2 and 3 show one of these nozzleassemblies in side-section and cutaway perspective views.

Each nozzle assembly comprises a nozzle chamber 24 formed by MEMSfabrication techniques on a silicon wafer substrate 2. The nozzlechamber 24 is defined by a roof 21 and sidewalls 22 which extend fromthe roof 21 to the silicon substrate 2. As shown in FIG. 1, each roof isdefined by part of a nozzle plate 56, which spans across an ejectionface of the printhead. The nozzle plate 56 and sidewalls 22 are formedof the same material, which is deposited by PECVD over a sacrificialscaffold of photoresist during MEMS fabrication. Typically, the nozzleplate 56 and sidewalls 21 are formed of a ceramic material, such assilicon dioxide or silicon nitride. These hard materials have excellentproperties for printhead robustness, and their inherently hydrophilicnature is advantageous for supplying ink to the nozzle chambers 24 bycapillary action.

Returning to the details of the nozzle chamber 24, it will be seen thata nozzle opening 26 is defined in a roof of each nozzle chamber 24. Eachnozzle opening 26 is generally elliptical and has an associated nozzlerim 25. The nozzle rim 25 assists with drop directionality duringprinting as well as reducing, at least to some extent, ink flooding fromthe nozzle opening 26. The actuator for ejecting ink from the nozzlechamber 24 is a heater element 29 positioned beneath the nozzle opening26 and suspended across a pit 8. Current is supplied to the heaterelement 29 via electrodes 9 connected to drive circuitry in underlyingCMOS layers of the substrate 2. When a current is passed through theheater element 29, it rapidly superheats surrounding ink to form a gasbubble, which forces ink through the nozzle opening 26. By suspendingthe heater element 29, it is completely immersed in ink when the nozzlechamber 24 is primed. This improves printhead efficiency, because lessheat dissipates into the underlying substrate 2 and more input energy isused to generate a bubble.

As seen most clearly in FIG. 1, the nozzles are arranged in rows and anink supply channel 27 extending longitudinally along the row suppliesink to each nozzle in the row. The ink supply channel 27 delivers ink toan ink inlet passage 15 for each nozzle, which supplies ink from theside of the nozzle opening 26 via an ink conduit 23 in the nozzlechamber 24.

The MEMS fabrication process for manufacturing such printheads wasdescribed in detail in U.S. Pat. No. 7,303,930, the contents of whichare herein incorporated by reference.

The operation of printheads having suspended heater elements isdescribed in detail in the Applicant's U.S. Pat. No. 7,278,717, thecontents of which are incorporated herein by reference.

The Applicant has also described thermal bubble-forming inkjetprintheads having embedded heater elements. Such printheads aredescribed in, for example, U.S. Pat. No. 7,246,876 and US 2006/0250453,the contents of which are herein incorporated by reference.

The Applicant's thermal inkjet printheads may be generally characterizedby having one or more of the following features: (i) suspended heaterelement; (ii) heater element having a mass of less than 1 nanogram,optionally less than 500 picograms; (iii) actuation energy of less than500 nJ, optionally less than 200 nJ; and (iv) titanium nitride ortitanium aluminium nitride heater element.

The solvent-based ink compositions of the present invention workoptimally in combination with the Applicant's thermal inkjet printheads,as described above. However, their use is not limited to the Applicant'sthermal printheads. The solvent-based ink compositions described hereinmay also be used in conventional thermal bubble-forming inkjetprintheads, such as those sold commercially by Hewlett-Packard andCanon.

In the case of conventional scanning thermal inkjet printheads (or,indeed, the Applicant's pagewidth printheads), the present invention mayrelate to an ink cartridge for a inkjet printer comprising any of thesolvent-based ink compositions described above. The ink cartridge mayoptionally comprise a thermal inkjet printhead integrated withtherewith.

For the sake of completeness, printers incorporating the Applicant'sthermal inkjet printheads are described in, for example, U.S. Pat. Nos.7,201,468; 7,360,861; 7,380,910; and 7,357,496, the contents of each ofwhich are herein incorporated by reference.

FIG. 4 shows a print engine 103 for a thermal inkjet printer, asdescribed in Applicant's U.S. application Ser. No. 12/062,514, thecontents of which is herein incorporated by reference. The print engine103 includes a removable print cartridge 102, comprising a pagewidthprinthead, and a bank of user-replaceable ink cartridges 128. Each colorchannel typically has its own ink reservoir 128 and a correspondingpressure-regulating chamber 106 for regulation of a hydrostatic pressureof ink supplied to the printhead. Hence, the print engine 103 has fiveink reservoirs 128 and five corresponding pressure-regulating chambers106. Typical color channel configurations for this five-channel printengine 103 are CMYKK or CMYK(IR). Each ink cartridge 128 may comprise asolvent-based ink composition as described herein. Accordingly, theprinter is suitable for printing onto non-porous (e.g. vinyl)substrates.

Although fluidic connections between the various components are notshown in FIG. 4, it will be appreciated that these connections are madewith suitable hoses in accordance with the fluidics system described in,for example, U.S. application Ser. No. 12/062,514.

It will further be appreciated that, whilst ink compositions accordingto the present invention were designed for use in thermal inkjetprintheads, they may also be useful in other types of inkjet printhead,such as the Applicant's bend-actuated inkjet printheads described in,for example, U.S. Pat. Nos. 7,416,280; 6,902,255; US 2008/0129793; andUS 2008/0225082, the contents of which are herein incorporated byreference.

EXPERIMENTAL

Evaluation of Bubble-Forming Solvents

Using an “open pool boiler” test apparatus, and after evaluating a widerange of solvents, the solvents described in Table A were shown togenerate bubbles in a thermal inkjet device. (An “open pool boiler” testapparatus essentially comprises one or more inkjet nozzles as shown inFIG. 2 without the roof structure 21).

Some physical characteristics of each solvent are also provided in TableA.

TABLE A Solvents generating bubbles in thermal inkjet test deviceSurface Evaporation Viscosity tension Solvent name Other name BPT (° C.)rate* (cP) (dynes/cm) MEK Methyl ethyl 80 4.03 0.43 24.18 ketoneDipropylene Di(propylene 187 0.02 3.44 28.25 glycol methyl glycol)methyl ether (DPM) ether, mixture of isomers Butyl DiGlycol 2-(2-Butoxy245 0.001 3.6 30.5 Acetate ethoxy) ethy acetate Methoxy Propyl Propylene145 0.33 1.2 28.2 Acetate glycol monomethyl ether acetate CyclohexanoneCyclohexanone 155 0.3 2 34 Carbitol Acetate Di ethylene 219 0.008 2.6731.4 glycol monoethyl ether acetate Hexyl acetate Hexyl acetate 1700.208 0.9 27.3 N-Methyl-2 1-Methyl-2- 202 0.03 1.65 40.1 Pyrrolidonepyrrolidone Ethanol Ethyl alcohol 78 1.7 1.1 22.18 Water 100 0.36 0.9 72(comparative) *relative to n-butyl acetate which has a value of 1.

Although all solvents listed in Table A generated bubbles in the testdevice, it was observed that the addition of ethanol to each solventsignificantly improved bubble formation.

A preferred solvent combination providing excellent bubble formation wasN-methyl-2-pyrrolidine (NMP) and ethanol in a 1:1 ratio.

Adhesion of Solvents to Vinyl

Each of the solvents listed in Table A was tested for adhesion to avinyl surface. Four large drops of solvent were placed on uncoated vinyland left for 60 seconds under ambient conditions. The solvents werewiped gently with a tissue and any mark on the vinyl surface was noted.

With the exception of water and ethanol, all solvents listed in Table Aleft a film impression on vinyl. The solvents are listed below in orderof the severity with which a film impressions was left on the vinylsurface.MEK>NMP>Cyclohexanone>>Hexyl acetate=Carbitol acetate=Butyldiglycolacetate=Methoxypropyl acetate>Dipropylene glycol methyl etherFilm Properties of Single Solvent Ink Compositions

In a further adhesion test, ink compositions were formulated consistingof a single solvent (from Table A) and a dye. Each ink compositionconsisted of: 97 wt. % solvent and 3 wt. % Bricosol red K10B (SolventRed 8).

The inks were applied as 6 micron wet films to the vinyl surface. Waterrubs, adhesion and appearance were noted. In general, all inkcompositions had a good film appearance on the vinyl surface beforetesting, with the exception of the carbitol acetate and hexylacetatecompositions, which exhibited some minor irregularities.

Water rubs were performed using cotton buds dipped in water, which werethen rubbed across the films. The number of rubs needed to damage thefilm was noted or, if no damage observed, stopped at 100 rubs. All inkcompositions showed excellent resistance to the water rub test, havingno significant change after>100 water rubs. (Usually, a number ofrubs>50 is considered to be excellent).

Adhesion tests were made by using a razor blade to mark six verticallines crossed by six horizontal lines in a grid (cross hatch). Scotch®tape was then placed over the grid and removed rapidly. The damage (ifany) to the film was noted and a given an adhesion rating: 0 (poor)-5(excellent). All ink compositions had an adhesion rating of 5.

The drying time of each film at room temperature was also noted and theresults are shown in Table B:

TABLE B Drying time of various single solvent ink compositions on vinylInk Composition Solvent Drying Time 1 cyclohexanone <10 s 2dipropyleneglycol methyl ether >120 s  3 butyldiglycol acetate >120 s  4methoxypropyl acetate  20 s 5 carbitol acetate >120 s  6 hexyl acetate<20 s 7 N-methyl pyrrolidinone <10 s

By way of comparison, a standard solvent-based piezo cyan ink wasmeasured to have a drying time of>120 s under the same test conditions.

In all ink compositions prepared, the water resistance and adhesion tovinyl were excellent, and performed at least as well as a piezosolvent-based standard.

On the basis of bubble formation and film properties, an ink compositioncomprising NMP and ethanol in a 1:1 ratio was considered to be anexcellent composition for thermal inkjets. However, all ink compositionscomprising an adhesion-promoting solvent and ethanol were considered tobe suitable for ejection using a thermal inkjet device and, indeed,showed good drop ejection characteristics from such a device.

Addition of Film Appearance Improvers

Several ink compositions were prepared using the preferred solventsystem of NMP and ethanol, and additionally including a nonionicsurfactant (Zonyl® FSO). These ink compositions are described in TableC.

TABLE C Ink compositions comprising NMP, ethanol, colorant andsurfactant With Zonyl FSO SBOB1- SBOB1- SBOB1- SBOB1- Code Other nameFunction 17-1 Blue 17-2 Red 17-3 Yellow 17-4 Black N-Methyl-21-Methyl-2- Solvent 48.4 48.4 48.4 48.4 Pyrrolidone pyrrolidone Solvent48.4 48.4 48.4 48.4 Ethanol Zonyl FSO Surfactant 0.2 0.2 0.2 0.2Bricosol red K10B Solvent red 8 dye colourant 3 Bricosol blue K2GVSolvent blue 70 dye colourant 3 Bricosol yellow KRV Solvent yellow 82dye colourant 3 Bricosol black NB Solvent black 27 dye colourant 3 Total100 100 100 100

Each ink composition was placed in a suitable ink reservoir and printedonto vinyl using a thermal inkjet printhead of the type described above,having suspended beam heater elements. All printouts had excellent filmappearance, water resistance and adhesion to the vinyl surface.

The addition of surfactant improved the film appearance of the ink onvinyl, compared to ink compositions in which the surfactant was absent.

Other surfactants shown to have a beneficial effect in improving thefilm appearance of printouts on vinyl were Tego Wet® 450, Tegoglide®410, Twin® 400, Tego Wet® 270 and Tegoglide® 482.

Similarly, incorporation of a vinyl polymer into the ink compositionshowed some improvement in the film appearance of printouts. Forexample, the addition of UCAR™ VYHH (a high molecular weight copolymerof vinyl chloride and vinyl acetate) to the ink compositions improvedthe film appearance of printouts onto a vinyl substrate. However,polymer additives were not considered to be essential for acceptablefilm appearance on vinyl print media.

Pigment Colorants

A CMYK set of inks was prepared using pigment dispersions combined withhexyl acetate solvent. The ink compositions are described in Table D.

TABLE D Ink compositions comprising pigments Pigment content SB0B1-SB0B1- SB0B1- SB0B- Code Other name Function (dispersion) 23-1 23-2 23-31-23-4 Hexyl acetate Solvent 80 84.3 81 82 S JD-C254 pigment Pigment 16%20 15:3 dispersion SJD R019 pigment Pigment 19% 15.7 V19 dispersionSJD-Y251 pigment Pigment 18% 18.75 Y151 dispersion SJD-BK17 pigmentPigment 17% 17.65 P K-7 dispersion Total 100 100 100 100

In all four colors, adhesion to vinyl and water resistance were shown tobe excellent. Furthermore, jettable ink compositions could be preparedusing ink compositions according to the present invention and comprisingpigment-based colorants.

It will, of course, be appreciated that the present invention has beendescribed by way of example only and that modifications of detail may bemade within the scope of the invention, which is defined in theaccompanying claims.

1. A solvent-based ink composition for a thermal inkjet printhead, saidink composition comprising: (a) 20-80 wt. % of a compound of formula(C);

wherein: R⁷ is a C₂₋₁₂ alkyl group interrupted with 0, 1, 2 or 3 oxygenatoms; (b) 10-70 wt. % of a C₁₋₆ alcohol; and (c) 0.01-25 wt. % of acolorant, wherein said composition does not comprise and polymers. 2.The ink composition of claim 1, wherein R⁷ is a C₄₋₈ alkyl groupinterrupted with 0, 1 or 2 oxygen atoms.
 3. The ink composition of claim1, wherein said compound of formula (C) is selected from the groupconsisting of: hexyl acetate; carbitol acetate; butyldiglycol acetate;and methoxypropyl acetate.
 4. The ink composition of claim 1, whereinsaid C₁₋₆ alcohol is ethanol.
 5. The ink composition of claim 1, whereinsaid colorant is a dye or a pigment.
 6. The ink composition of claim 1,further comprising: 0.001-10 wt. % of a surfactant.
 7. The inkcomposition of claim 6, wherein said surfactant is a nonionicsurfactant.
 8. The ink composition of claim 1, consisting essentially ofsaid compound of formula (C), said C₁₋₆ alcohol and said colorant. 9.The ink composition of claim 1, consisting only of said compound offormula (C), said C₁₋₆ alcohol and said colorant.
 10. The inkcomposition of claim 1, consisting only of said compound of formula (C),said C₁₋₆ alcohol, said colorant and 0.01-10 wt. % of a surfactant. 11.An ink cartridge for a thermal inkjet printhead, said ink cartridgecontaining the solvent-based ink composition according to claim
 1. 12.The ink cartridge of claim 11, wherein said ink cartridge comprises saidthermal inkjet printhead integrated therewith.
 13. A substrate having anink composition according to claim 1 disposed thereon.
 14. The substrateof claim 13, which is a semi-porous or non-porous substrate.
 15. Thesubstrate of claim 13, which is a vinyl substrate.